Such a rotary regenerator, commonly referred to as a heat exchange "wheel", is mounted spanning across, and for rotation between adjacent but separate gas supply and exhaust ducts. The wheel is primarily constituted by a gas-permeable matrix or medium through which both the incoming and outgoing streams pass. The matrix is capable of absorbing moisture and/or thermal energy from one gas stream for subsequent release, upon further rotation, into the second gas stream. For instance, if it is desired to heat and humidify an incoming fresh air stream in a building air supply system during the winter season, the wheel abstracts both sensible and latent heat energy from the warmer and moister exhaust air stream which is flowing oppositely in the adjacent exhaust duct by exposing the wheel matrix thereto, whereupon the wheel rotates to expose the matrix area and thus transfer the sensible and latent heat energy to the cooler, drier incoming air flowing in the supply duct. Conversely, in the summer season, there is a need to remove moisture and heat from the incoming air stream for use in the air-conditioned building and, under these circumstances, the matrix first absorbs sensible and latent energy from the incoming air, whereupon the wheel is rotated into the cooler, drier exhaust air stream which absorbs the sensible and latent energy from the wheel matrix and discharges such energy outside the air-conditioned spaces. Thus, the device substantially reduces the amount of heat energy and moisture required to be added to warm the incoming fresh air in wintertime, and the amount of cooling and dehumidification of the fresh air which would otherwise be required in the summertime.
One material which has been used as the heat transfer medium in such total heat energy exchange wheels is asbestos in the form of alternately flat and corrugated asbestos paper sheets which are impregnated with an hygroscopic salt such as lithium bromide or lithium chloride for improved transfer of moisture. Although such heat and moisture exchange media have also been made of cellulosic paper as shown for example in Canadian Pat. No. 629,879 (Munters), or of coated or specially treated paper to remove latent or sensible heat transfer capabilities or to improve strength as shown for example in U.S. Pat. No. 3,664,095 (Asker et al), asbestos has been considered generally superior to paper or other material, at least in terms of the latent heat and moisture exchange rates and efficiencies of comparably sized media. See, for example, U.S. Pat. No. 3,398,510 (Pennington) in which a comparison is made between the characteristics of cellulosic paper and asbestos paper in such wheels, albeit as used for moisture transfer rather than for total heat exchange.
However, for various reasons it is desirable in particular instances of use to provide a total heat energy exchange medium made from material other than asbestos, but whose latent and sensible heat energy exchange efficiencies approximate to those of such impregnated asbestos material. It is an object of the present invention to provide such an alternative heat exchange medium.
It should be noted that all-metal media wheels, formed by spirally winding either stainless steel foil or aluminum foil about a hub as can be seen for instance in U.S. Pat. No. 3,702,156 (Rohrs et al) and Canadian Pat. No. 629,879 (Munters), are commonly employed where it is intended to recover and exchange only sensible heat. Such metal wheels are obviously not capable of recovering and transferring significant latent heat energy or moisture.
Of course, a suitable energy exchange medium or matrix should have not only both latent and sensible heat exchange efficiencies comparable to those of a matrix made of asbestos impregnated with an hygroscopic substance such as lithium chloride, but must also satisfy other requirements of such devices, and it is intended by the present invention to provide such an energy exchange device which meets all such criteria. For example, the device and therefore its energy exchange matrix material and construction must be substantially fire resistant and bacteriostatic, and have adequate strength and erosion resistance for its intended use, such as in an airstream flowing at moderate or even high velocity on the order of from about from about 500 feet per minute (fpm) to about 1000 fpm. It must be convenient to manufacture, and its manfacturing costs should approximate those of an asbestos wheel.